The start dates seem to have ranged roughly from within the last month right through until next summer (June is the latest I'm aware of, but I'm not clear on the dates with OAA or CTC). Obviously for some people this will allow them to finish degrees, etc. This worked out nicely for me as my current job is very busy through the summer and much quieter in the winter. That said, being stuck up a mountain in the snow isn't so bad when you're getting paid for it!
Just to be clear, though; neither does anyone get to directly choose a start date, nor can you simply elect to swap. I think this would be entirely at the discretion of the various companies involved and likely under exceptional circumstances. Don't quote me on it, though! There are various opportunities during the recruitment phases to state at which point you would be available to commence training, if successful.
Incidentally, I agree with you about CforE with regard to primary education. Have plenty of teacher friends and it's mostly the high school ones who're complaining. That said, they complained a fair amount before the new system was even suggested.
